Abstract: Microfiltration(0.8,0.2 μm) and ultrafiltration(50 nm) were used respectively to treat black liquor from wheat-straw pulp.The effects of operation conditions on the permeate flux of inorganic membrane were explored.It was showed that the adoption of membrane with 0.2 μm or 0.8 μm pore size was favorable to the improvement of permeate flux and the keeping of the membrane permeability.Higher permeate flux could be obtained under the condition of TMP 0.25～0.35 MPa,crossflow velocity ≥5 m/s and temperature 60 ℃. The characteristics of black liquor itself,such as the concentration and COD,could also have major impact on permeate flux.